The invention relates to a process and a device for implementing the process for the transport of workpieces or workpiece carriers in transfer lines or transfer machines with an arbitrary and also changeable number of stations.
Transfer lines and transfer machines are installations in which workpieces or workpiece carriers are transported from a first station via all other stations to a last station. Normally, in particular, the workpiece carriers must, after their passage, arrive again at the first station,in order to again be entered into the timing of the system. Essentially two methods are known which meet this requirement. The first method is the revolving method carried out by means of the revolving machine which, because of its arrangement, guides the workpieces and workpiece carriers in a circle so that the last station is directly adjacent to the first station. A related form is the transfer line in which the stations are arranged such that the last station is also adjacent to the first station. The second method is the normally linear transfer on transfer lines or on transfer machines in the case of which the last station has a distance from the first station which corresponds approximately to the machine length. For this reason, a return transport must be organized which, in the case of the known constructions, takes place along a different path than the forward transport.
A disadvantage of the revolving machine is the number of stations which are determined as a function of the diameter of the circle and allow no flexibility concerning the increase or decrease of the number of stations. In addition, it often ties up an excessive number of workpiece carriers because the number of its stations may be larger than the number of its productive working stations. Finally, its accessibility is severely limited because of the shape which is closed because it is round. The disadvantage of the linear transfer line or transfer machine is the transport device which is additionally required for the return transport. It results in a doubling of the transport path and thus to an increase of the revolving workpiece carriers.
From German Patent Document DE 39 18 235 A1, an arrangement is known for transfer lines in the case of processing machines which are equipped with conveying tongs for the timed transfer of the workpieces from one station to the next. In order to compensate processing times of different lengths of individual stations, in the case of the object of German Patent Document DE 39 18 235 A1, a second processing plane is provided which extends in parallel to the timed transfer plane. After two or more timed steps in the transfer plane, two or more workpieces are simultaneously brought from the transfer plane to the longer operating stations in the parallel second processing plane. In this case, the forward and return transfer of the workpieces to be further processed or have already been further processed takes place by means of transfer devices arranged between the two planes irrespective of the timed steps in the transfer plane. Thus, the arrangement of additional transfer devices and the arrangement of a second processing plane are not necessary.
The invention described here avoids the above-mentioned disadvantages. It is based on the object of minimizing the workpieces or workpiece carriers revolving in the system. By means of the invention, preferably linear transfer systems are to be constructed in a modular manner, in which case their number of stations can be increased or reduced arbitrarily. In addition, the invention must not require any special devices for the return transport of the workpieces or workpiece carriers.
According to the invention, this object is achieved in that the forward transport of the workpieces or workpiece carriers from the first station via all subsequent stations to an arbitrary, preferably last station, takes place by means of swivellable transfer devices which are arranged between adjacent stations, and the return transport from this station back to the first station takes place in a continuous flow by an alternating transfer in pairs by means of the same transfer devices and on the same path.
The technical elements which implement the process are dumbbell-type double arms with controllable fastening elements for the workpieces or workpiece carriers to be transferred. These double arms are controlled by a control, preferably a stored-program control (SPC) or a computerized numerical control (CNC), in such a manner that, of the continuously numbered double arms, alternately only the even-numbered or only the odd-numbered double arms are used for the transfer. The total number of dumbbell-type double arms in the transfer line or transfer machine is by 1 smaller than the number of stations. The construction of the transfer line or transfer machine is preferably linear.
In the following, the method of operation of the invention will be explained by means of embodiments which are illustrated in the drawings.